As integrated circuit feature sizes shrink, memories embedded within an integrated circuit increase in density, and become more prone to failure. These failures reduce yield, resulting in higher cost per unit produced. One method of improving embedded memory yield involves including spare memory cells in the integrated circuit to replace memory cells found to be defective when the chip is tested. Employing redundancy in this manner can significantly improve the yield of embedded memories with minimal investment in die area.
“Fuse farms” are utilized as part of a system of embedded memory redundancy. A non-volatile memory in the fuse farm stores all the information necessary to repair embedded memories by replacing faulty memory cells with spare cells. During device initialization, a controller in the fuse farm reads the repair information from the fuse farm non-volatile memory (“fuse ROM”) and loads the repair information into the on-chip embedded memories.
Being a form of embedded memory, the fuse ROM is itself subject to an increased rate of failure with reduced feature size. Because the fuse farm supplies repair information for the on chip memories, a fault in the fuse farm memory may result in a die that must be discarded. Moreover, users may be permitted to store limited information, such as serial numbers or part identifiers in fuse ROM after the part leaves the manufacturing facility. The fuse ROM may be implemented in a non-erasable memory technology, making pre-shipment testing of the fuse ROM impossible, and subjecting the manufacturer to an increased risk of loss of customer goodwill if the device is discarded due to an in-field fuse ROM programming failure.